Silicides are alloys of silicon and metals. Silicides combine the advantageous features of metal contacts (e.g significantly lower resistivity than poly-Si) and poly-Si contacts (e.g. no electromigration and the ability to withstand subsequent high temperature processes), and have been widely used in semiconductor devices. For example, forming silicide contacts in SiC devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), static induction transistors (SITs), junction gate field-effect transistors (JFETs), metal-semiconductor field effect transistors (MESFETs), diodes, and bipolar junction transistors (BJTs), is an accepted method for reducing contact resistance and improving device performance.
Nickel silicide is the most common silicide used in SiC devices because of its low contact resistance to n+ material. However, nickel silicide is known to agglomerate during formation as well as produce stringers when formed on SiC. Agglomeration primarily occurs in large area contacts and degrades the contact resistance and possibly device reliability as well. Stringer formation can be even more problematic, as these stringers can cause shorting, particularly in structures with sub micron features. The tendency to form these stringers or agglomeration has not been well understood. FIG. 1 shows two examples of stringer formation, demonstrating that stringers can be rather small in some incidences, and very large and long in some other incidences, depending on the vagaries of the processing. The formation of stringers lead to difficulties in managing product yield when processing SiC devices.
Therefore, there still exists a need for methods of forming silicide contacts with reduced stringers.